The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.
Blood oxygen saturation (SpO2) refers to a fraction of oxygen-saturated hemoglobin relative to total hemoglobin in the blood. Decreased SpO2 in the blood can lead to impaired mental function, or loss of consciousness, and may serve to indicate other serious health conditions, such as sleep apnea or cardiovascular disease. Therefore, accurately measuring SpO2 is important in certain kinds of health monitoring.
Methods for measuring SpO2 in the blood include invasive procedures, such as drawing blood, and noninvasive methods of monitoring SpO2, such as through reflectance-based pulse oximetry. Reflectance-based pulse oximetry is a technique for monitoring SpO2 by detecting the volumetric change of aerial blood vessels using photoplethysmography (PPG) with wavelengths in the red and infrared regions.
Pulse oximetry tends to be most effective when performed on areas of the body where blood vessels are close to the surface of the skin, such as the fingertip or forehead. While pulse oximetry tends to be most effective in these areas, devices for monitoring SpO2 through pulse oximetry on the fingertip or forehead can be cumbersome. If a person wishes to monitor SpO2 throughout the day, a device on the fingertip or forehead may be impractical.
In terms of wearing a device capable of measuring SpO2, a user may prefer to wear such a device on other parts of the body, like on their wrist, which may be the case especially if the user is wearing the device for extended periods of time. However, measuring SpO2 through pulse oximetry tends to be more difficult on these other body parts. Differences in skin morphology can cause light emitters to be less effective for some people than others. For instance, a person may have a mole or hair that covers a light emitter, thereby decreasing the quality of the signal received by the detector. The presence of cosmetic features such as tattoos also can affect signal quality. In addition, when blood vessels are further from the skin surface, or when there is low blood perfusion due to cool skin temperature, the presence of fatty tissue or other morphology such as cardiovascular disease, signal noise may decrease the quality of the received PPG signals.